Load control device for controlling a driver for a lighting load

ABSTRACT

If there is an interruption of power to an electrical load while the electrical load is operating at low end, the electrical load may not turn back on when power is restored. This undesired operation may be avoided by detecting the application of power to the electrical load, and automatically increasing the magnitude of a control signal being applied to the electrical load by a sufficient amount for a short period of time after power has been applied. This way, the electrical load may be turned back on to low end, instead of erroneously operating in an electronic off condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 16/183,565, filed Nov. 7, 2018, which is a continuation of U.S. patent application Ser. No. 15/713,543, filed Sep. 22, 2017, issued as U.S. Pat. No. 10,149,355 on Dec. 4, 2018, which claims priority to Provisional U.S. Patent Application No. 62/398,636, filed Sep. 23, 2016, the disclosures of which are incorporated herein by reference in their entireties.

BACKGROUND

A lighting source, such as a light-emitting diode (LED) light source, is typically driven by a load regulation device (e.g., such as an LED driver) in order to illuminate. A common control method for dimming an LED light source controlled by an LED driver is “zero-to-ten-volt” (0-10V) control, which is sometimes referred to as 1-10V control. A 0-10V LED driver receives power from an AC power source, with an external mechanical switch typically coupled between the AC power source and the 0-10V driver to provide a switched-hot voltage to the driver. Alternatively, the switched-hot voltage may be generated by an external power device (e.g., a power pack). The 0-10V driver controls the intensity of the connected LED light source in response to a 0-10V control signal received from a 0-10V control device (e.g., a 0-10V controller). Often, the 0-10V control device is mounted in an electrical wallbox and comprises an intensity adjustment actuator (e.g., a slider control). The 0-10 V control device regulates the direct-current (DC) voltage level of the 0-10V control signal provided to the driver between a substantially low voltage (e.g., zero to one volt) to a maximum voltage (e.g., approximately ten volts) in response to an actuation of the intensity adjustment actuator. For example, the 0-10V driver may control the intensity of the LED light source to a low-end intensity L_(LE) (e.g., approximately 0.1%-10%) when the DC voltage level of the 0-10V control signal is at the substantially low voltage (e.g., zero to one volt) and to a high-end intensity L_(HE) (e.g., approximately 100%) when the DC voltage level of the 0-10V control signal is at the maximum voltage (e.g., approximately ten volts).

To turn off the LED light source controlled by the 0-10V driver, power is removed from the 0-10V driver by, for example, controlling the switched-hot voltage to zero volts. The 0-10V control device may comprise a switching circuit for generating the switched-hot voltage. The switching circuit may include, for example, a mechanical air-gap switch, a relay, and/or a bidirectional semiconductor switch, such as a triac, one or more silicon-controlled rectifiers (SCRs), a field-effect transistor (FET) in a rectifier bridge, two FETs in anti-series connection, one or more insulated-gate bipolar junction transistors (IGBTs), or any suitable semiconductor switching circuit. In some cases, the 0-10V control device may be powered via the 0-10V control wires, for example, by drawing current from the 0-10V driver. Prior art 0-10V drivers typically source between 1-2 milliamperes of current, which the 0-10V control device may use to power itself.

Some 0-10 V drivers may be responsive to occupancy sensors, vacancy sensors, and/or daylight sensors. If the switched-hot voltage is controlled to zero volts to turn off the LED light source (e.g., by opening the switching circuit of the 0-10V control device or the power pack), the 0-10V driver will then be unpowered and unable to respond to the occupancy sensors, vacancy sensors, and/or daylight sensors.

Rather than removing power from an 0-10V driver to turn off the LED light source, the 0-10V driver may be controlled to an electronic off (e.g., standby) state in which the 0-10V driver remains powered, but turns off the LED light source. The 0-10V driver may be configured to change between an on state and the electronic off state in response to the 0-10V signal (e.g., using hysteresis). For example, during the on state, the 0-10V control device may be configured to adjust the DC voltage level of the 0-10V control signal between a minimum level (e.g., approximately 0.61-1.00 volts) and a maximum level (e.g., approximately ten volts) to adjust the intensity of the LED light source between the low-end intensity L_(LE) and the high-end intensity L_(HE), respectively. To control the 0-10V driver into the electronic off state, the 0-10V control device may be configured to adjust the DC voltage level of the 0-10V control signal to a standby level. For example, the 0-10V driver may be configured to change to the electronic off state when the DC voltage level of the 0-10V control signal drops below a falling threshold (e.g., approximately 0.6 V). The 0-10V driver may be configured to return to the on state (e.g., to turn on) when the DC voltage level of the 0-10V control signal rises above a rising threshold (e.g., approximately 1.0 V), after which the 0-10V driver may adjust the intensity of the LED light source between the low-end intensity L_(LE) and the high-end intensity L_(LE) as the 0-10V control signal ranges between the minimum level and the maximum level.

Since the falling threshold may be approximately 0.6 V, the DC voltage level of 0-10V control signal may be as low as 0.61 V when the 0-10V driver is being controlled to the low-end intensity L_(LE). This means that the DC voltage level of 0-10V control signal at the low-end intensity L_(LE) may be between the rising threshold and the falling threshold. If there is a momentary interruption of the power, such as a power outage or a manual switch-off of power to the 0-10V driver when the 0-10V driver is in the on state, and the DC voltage level of the 0-10V control signal is between the rising threshold and the falling threshold, the 0-10V driver may not turn back on when power is restored (e.g., re-applied) because the DC voltage level of 0-10V control signal will not be above the rising threshold. It is undesirable for a lighting load that is on to not turn back after a momentary power interruption.

SUMMARY

As described herein, a load control device for controlling an amount of power delivered to a lighting load may comprise a communication circuit configured to generate a control signal for controlling the amount of power delivered to the lighting load. The control signal may cause the lighting load to be turned on when the magnitude of the control signal rises above a threshold. The load control device may also comprise a control circuit configured to control the communication circuit to adjust the magnitude of the control signal so as to adjust an intensity of the lighting load between a low-end intensity and a high-end intensity. The magnitude of the control signal may be less than the threshold when the intensity of the lighting load is being controlled to the low-end intensity. When power has been applied to the lighting load, the control circuit may be configured to determine that a desired magnitude of the control signal is below the threshold, and increase the magnitude of the control signal to be equal to or greater than the threshold before decreasing the magnitude of the control signal to the desired magnitude.

The load control device described herein may include an intensity adjustment actuator and a potentiometer circuit responsive to the intensity adjustment actuator for determining the desired magnitude of the control signal. The load control device may further include a sense circuit configured to provide an indication of when power has been applied to the lighting load. Once power has been applied to the lighting load and the magnitude of the control signal is set to be equal to or greater than the threshold, the control circuit of the load control device may cause the magnitude of the control signal to be decreased to the desired magnitude over a first period of time. The control circuit may maintain the magnitude of the control signal constant at a level equal to or greater than the threshold for a second period of time before decreasing the magnitude of the control signal to the desired magnitude over the first period of time.

Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example 0-10V load control device.

FIG. 2 is a simplified flowchart of a voltage sense procedure that may be executed by a microprocessor of a control circuit of the load control device of FIG. 1.

FIG. 3 is a simplified diagram of example waveforms illustrating the operation of the load control device during the voltage sense procedure of FIG. 2.

FIG. 4 is a simplified block diagram of another example 0-10V load control device.

FIG. 5 is a simplified diagram of example waveforms illustrating the operation of a bump-up circuit of the load control device of FIGS. 4.

DETAILED DESCRIPTION

Described herein are examples of a load control system for controlling the amount of power delivered to an electrical load, such as a lighting load, and more particularly, of a wall-mounted load control device for controlling a load regulation device, such as an LED driver for an LED light source, via a control signal, such as a 0-10V control signal.

FIG. 1 is a simplified block diagram of an example 0-10V load control device 100. The load control device 100 may comprise a hot terminal H adapted to be coupled to an AC power source 102 and a switched hot terminal SH adapted to be coupled to an electrical load. The electrical load may comprise a load regulation circuit for driving a lighting load, such as an LED driver 104 for controlling an LED light source 106. In an example, the load control device 100 may comprise a neutral terminal N adapted to be coupled to the neutral side of the AC power source 102. In another example, the load control device 100 may not require connection to the neutral side of the AC power source 102 via the neutral terminal N (e.g., the load control device may be a “two-wire” load control device).

The load control device 100 may comprise first and second control terminals C1, C2 adapted to be coupled to the LED driver 104 via a control wiring 108. The LED driver 104 may be configured to control the power delivered to the LED light source 106, and thus the intensity of the LED light source 106, in response to a direct-current (DC) control signal V_(CS) received from the load control device 100 via the control wiring 108. For example, the LED driver 104 may be configured to turn the LED light source 106 on and off, and/or to adjust the intensity of the LED light source 106 between a low-end (e.g., minimum) intensity L_(LE) and a high-end (e.g., maximum) intensity L_(HE) in response to the control signal V_(CS). The LED driver 104 may be configured to control the power delivered to the LED light source 106, for example, by regulating the voltage generated across the LED light source 106 and/or regulating the current conducted through the LED light source 106. Examples of an LED driver are described in greater detail in commonly-assigned U.S. Pat. No. 8,492,987, issued Jul. 23, 2013, entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE, and U.S. Pat. No. 9,232,574, issued Jan. 5, 2016, entitled FORWARD CONVERTER HAVING A PRIMARY-SIDE CURRENT SENSE CIRCUIT, the entire disclosures of which are hereby incorporated by reference. Although described as an LED light source driven by an LED driver, the electrical load referenced herein may comprise an electronic ballast for driving a fluorescent lamp.

The load control device 100 may comprise a switching circuit 110, which may be electrically coupled in series between the hot terminal H and the switched hot terminal SH. The switching circuit 110 may be rendered conductive and non-conductive in response to actuations of an on/off actuator 112 (e.g., a toggle switch) to generate a switched-hot voltage V_(SH) at the switched hot terminal SH. The on/off actuator 112 may comprise a mechanical switch that is actuated by a slider control, for example, when the slider control reaches a minimum position (e.g., a “slide-to-off” slider control).

The load control device 100 may also include a driver communication circuit 114 that may comprise a current sink circuit adapted to sink current from the LED driver 104 via the control wiring 108. The LED driver 104 may be configured to generate a link supply voltage (e.g., approximately 10 V) to allow the current sink circuit of the driver communication circuit 114 to generate the control signal V_(CS) on the control wiring 108. The load control device 100 may comprise a power supply 116 coupled between the hot terminal H and the neutral terminal N for generating a DC supply voltage V_(CC) for powering the low-voltage circuitry of the load control device 100.

The load control device 100 may comprise a control circuit 120 (e.g., a digital control circuit) configured to control the driver communication circuit 114 to generate the control signal V_(CS) for adjusting the intensity of the LED light source 106. The control circuit 120 may include a microprocessor 122. The control circuit 120 could also include any suitable controller or processing device, such as, for example, a programmable logic device (PLD), a microcontroller, an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA). The microprocessor 122 may be configured to determine a desired light intensity L_(DES) for the LED light source 106 and a corresponding desired magnitude V_(DES) for the control signal V_(CS) in response to an intensity adjustment actuator 124 (e.g., a slider control). For example, the microprocessor 122 may be configured to receive a DC potentiometer wiper voltage V_(POT) from a potentiometer circuit 126, which may be responsive to the intensity adjustment actuator 124. The microprocessor 122 may be configured to control the magnitude of the control signal V_(CS) to the desired magnitude V_(DES) so as to adjust the intensity of the LED light source 106 to the desired light intensity L_(DES) (e.g., between a low-end intensity L_(LE) and a high-end intensity L_(HE)).

The microprocessor 122 of the control circuit 120 may generate a direct-current (DC) output signal V_(DC) and provide the output signal V_(DC) to the driver communication circuit 114. For example, the microprocessor 122 may comprise a digital-to-analog converter (DAC) for generating the DC output signal V_(DC) that is received by the driver communication circuit 114 for generating the control signal V_(CS). The microprocessor 122 may adjust the magnitude of the control signal V_(CS) by adjusting the magnitude of the output signal V_(DC). The output signal V_(DC) may comprise a pulse-width modulated (PWM) signal or variable-frequency waveform, in response to which the driver communication circuit 114 may be configured to adjust the magnitude of the control signal V_(CS). The driver communication circuit 114 may comprise a current source circuit or a current source/sink circuit for generating the control signal V_(CS) in response to the output signal V_(DC).

The LED driver 104 may be controlled to an electronic off (e.g., standby) state during which the LED driver 104 may turn off the LED light source while control circuitry of the LED driver remains powered. The LED driver 104 may be configured to change between an on state and the electronic off state in response to the control signal V_(LE) (e.g., using hysteresis). For example, during the on state, the control circuit 120 may be configured to adjust the DC voltage level of the control signal V_(CS) between a low-end magnitude V_(LE) (e.g., approximately 0.9 volts) and a high-end magnitude V_(HE) (e.g., ten volts) to adjust the intensity of the LED light source 106 between the low-end intensity L_(LE) and the high-end intensity L_(HE), respectively. To control the LED driver 104 into the electronic off state, the control circuit 120 may be configured to adjust the DC voltage level of the control signal V_(CS) to a standby level. For example, the LED driver 104 may be configured to change to the electronic off state when the DC voltage level of the 0-10V control signal drops below a falling threshold V_(TH-FALLING) (e.g., approximately 0.6 V). The LED driver 104 may be configured to return to the on state (e.g., to turn on) when the DC voltage level of the control signal V_(CS) rises above a rising threshold V_(TH-RISING) (e.g., approximately 1.0 V), after which the LED driver 104 may adjust the intensity of the LED light source 106 between the low-end intensity L_(LE) and the high-end intensity L_(HE) as the control signal V_(CS) ranges between the low-end magnitude V_(LE) and the high-end magnitude V_(HE).

During the on state, the low-end magnitude V_(LE) of the control signal V_(CS) may be less than the rising threshold V_(TH-RISING). For example, the low-end magnitude V_(LE) of the control signal V_(CS) may be approximately 0.9 V while the rising threshold V_(TH-RISING) may be approximately 1.0 V. If the LED driver 104 and the load control device 100 temporarily lose power while the load control device is controlling the intensity of the LED light source 106 to the low-end intensity L_(LE), the magnitude of the control signal V_(CS) (e.g., the low-end magnitude V_(LE)) may not exceed the rising threshold V_(TH-RISING) when power is restored and the LED driver 104 may not turn on the LED light source 106. Similarly, when the on/off actuator 112 is actuated to close the switching circuit 110 to turn the LED light source 106 on and the intensity adjustment actuator 122 is set to the low-end intensity L_(LE), the magnitude of the control signal V_(CS) may also not exceed the rising threshold V_(TH-RISING) and the LED driver 104 may not turn on the LED light source 106 when the LED driver 104 is switched on by the switching circuit 110.

Accordingly, the control circuit 120 may be configured to at least temporarily increase the magnitude of the control signal V_(CS) when power is applied (e.g., initially applied or re-applied) to the lighting load 106 (i.e., to the LED driver 104). For example, the control circuit 120 may be configured to temporarily increase the magnitude of the control signal V_(CS) to be equal to or above the rising threshold V_(TH-RISING) when power is applied to the LED driver after an interruption and the desired magnitude V_(DES) for the control signal V_(CS) is initially less than the rising threshold V_(TH-RISING). The power interruption may be caused by a power outage or a manual switch-off of the on/off actuator 112, for example. The control circuit 120 may comprise a voltage sense circuit 128 configured to generate a voltage sense signal V_(SENSE) that may indicate when power has been applied to the LED driver 104. For example, the voltage sense circuit 128 may be coupled between the switched hot terminal SH and the neutral terminal N to receive the switched-hot voltage V_(SH) as shown in FIG. 1. The voltage sense circuit 128 may be configured to drive the voltage sense signal V_(SENSE) high towards the supply voltage V_(CC) when the magnitude of the switched-hot voltage V_(SH) rises above a voltage sense threshold V_(TH-SENSE) (e.g., the voltage sense circuit 128 may comprise a comparator circuit). In an example, the control circuit 120 may be configured to determine that power has just been applied to the LED driver 104 in response to detecting a rising edge of the voltage sense signal V_(SENSE). In another example, the voltage sense signal V_(SENSE) may simply be a scaled version of the switched-hot voltage V_(SH) (e.g., the voltage sense circuit 128 may comprise a scaling circuit, such as a resistive divider), and the control circuit 120 may be configured to sample the voltage sense signal V_(SENSE) and compare the sampled magnitude to the voltage sense threshold V_(TH-SENSE) to determine when power has just been applied (or re-applied) to the LED driver 104.

While the switching circuit 110 and the on/off actuator 112 is shown in FIG. 1 as integral with the load control device 100, the switching circuit and/or the on/off actuator 112 could be external to the load control device 100 (e.g., the switching circuit could be included in an external light switch or an external switching power pack). In addition, the switching circuit 110 could comprise a relay controlled by the microprocessor 122 and the on/off actuator 112 could comprise a low-voltage switch (e.g., a mechanical tactile switch) for generating a low-voltage signal that is received by the microprocessor 122. The microprocessor 122 may be configured to detect that the low-voltage switch has been actuated, close the relay, and temporarily increase the magnitude of the control signal V_(CS) (e.g., without the need for the voltage sense circuit 128).

As described herein, power being applied (e.g., initially applied or re-applied) to the lighting load 106 may occur when power is restored after a temporary power interruption (e.g., by an electrical utility company), when the switching circuit 110 is closed, and/or when an external switching circuit (e.g., in a light switch or a switching power pack) coupled in series between the AC power source 102 and the lighting load 106 is closed. One of ordinary skill in the art will recognize that there are other ways that power may be applied to a lighting load.

FIG. 2 is a simplified flowchart of a voltage sense procedure 200 that may be executed by the microprocessor 122 of the control circuit 120 of the load control device 100. FIG. 3 is a simplified diagram of example waveforms illustrating the operation of the load control device 100 during the voltage sense procedure 200. The voltage sense procedure 200 may begin when the microprocessor 122 detects a rising edge of the voltage sense signal V_(SENSE) at step 210 indicating that power has just been applied to the LED driver 104 (e.g., as shown at time t_(RISING) in FIG. 3), e.g., after an interruption. The microprocessor 122 may then determine the desired magnitude V_(DES) for the control signal V_(CS) (e.g., using the desired light intensity L_(DES) determined from the intensity adjustment actuator 122) at step 212. If the desired magnitude V_(DES) is not less than the rising threshold V_(TH-RISING) at step 214, the microprocessor 122 may set the magnitude of the control signal V_(CS) to the desired magnitude V_(DES) at step 216, before the voltage sense procedure 200 exits. If the desired magnitude V_(DES) is less than the rising threshold V_(TH-RISING) at step 214, the microprocessor 122 may set the magnitude of the control signal V_(CS) to be equal to the rising threshold V_(TH-RISING) plus an offset voltage V_(OFFSET) at step 218. For example, the offset voltage V_(OFFSET) may be sized to ensure that the magnitude of the control signal V_(CS) is greater than the rising threshold V_(TH-RISING) when power is applied to the LED driver 104 (e.g., as shown at time t_(RISING) in FIG. 3) so as to drive the LED driver 104 to the on state. The microprocessor 122 may then fade (e.g., adjust) the magnitude of the control signal V_(CS) to the desired magnitude V_(DES) (e.g., the low-end magnitude V_(LE) as shown in FIG. 3) over a first period of time T_(FADE), which may be approximately 0.5-1 second, at step 220, before the voltage sense procedure 200 exits. While not shown in FIG. 2, the microprocessor 122 may hold the magnitude of the control signal V_(CS) equal to the rising threshold V_(TH-RISING) plus the offset voltage V_(OFFSET) for a second period of time before beginning to fade the magnitude of the control signal V_(CS) to the desired magnitude V_(DES) over the period of time T_(FADE).

The operation of the control circuit 120 in response to the application of power to the LED driver 104 may be controllable and/or programmable. For example, the control circuit 120 may be configured to adjust the magnitude of the offset voltage V_(OFFSET), and/or the length of the first and/or the second time period (e.g., the period of time T_(FADE)), in response to an external input (e.g., a programming input). The external input may be received, for example, from an actuation of the intensity adjustment actuator 124 and/or the on/off actuator 112, an actuation of one or more programming buttons (not shown), an actuation of one or more separate programming potentiometers (not shown), and/or one or more messages received via a communication circuit (not shown).

FIG. 4 is a simplified block diagram of another example of a 0-10V load control device 300. The load control device 300 may be configured to control an amount of power delivered to an electrical load. The electrical load may include, e.g., a load regulation circuit for driving the electrical load, such as an LED driver 304 for controlling an LED light source 306. The load control device 300 may or may not be electrically coupled in series between an AC power source 302 and the electrical load. The load control device 300 may comprise first and second control terminals C1, C2 adapted to be coupled to the LED driver 304 via a control wiring 308. The load control device 300 may comprise a communication circuit configured to generate a control signal for controlling power delivered to the LED lighting load 306. The load control device 300 may include, for example, a current sink circuit 310 electrically coupled to the control terminals C1, C2 for sinking current from the LED driver 104 via the control wiring 108. The current sink circuit 310 may be configured to generate a DC control signal V_(CS) for controlling the LED driver 304 to turn the LED light source 306 on and off, and to adjust the intensity of the LED light source 306 when the LED light source 306 is on.

The load control device 300 may comprise a control circuit 320 (e.g., an analog control circuit) configured to control the current sink circuit 310 to generate the control signal V_(CS) for turning the LED light source 306 on and off, and for adjusting the intensity of the LED light source 306. The control circuit 320 may comprise a potentiometer circuit 322 for generating a DC output signal V_(DC) in response to an intensity adjustment actuator 324 (such as, e.g., a slider control, a thumbwheel, or a knob). The potentiometer circuit 322 may provide the DC output signal V_(DC) to the current sink circuit 310 for controlling the magnitude of the control signal V_(CS) to a desired magnitude V_(DES) so as to adjust the intensity of the LED light source 306 to a desired light intensity L_(DES) (e.g., between a low-end intensity L_(LE) and a high-end intensity L_(HE)).

The LED driver 304 may be controlled to an electronic off (e.g., standby) state during which the LED driver 304 may turn off the LED light source while control circuitry of the LED driver remains powered (e.g., in a similar manner as the LED driver 104 shown in FIG. 1). The LED driver 304 may be configured to change between an on state and the electronic off state in response to the control signal V_(CS) (e.g., using hysteresis). For example, the LED driver 304 may be configured to change to the on state (i.e., to turn on) when the DC voltage level of the control signal V_(CS) rises above a rising threshold V_(TH-RISING) (e.g., approximately 1.0 V).

As with the load control device 100 of FIG. 1, the low-end magnitude V_(LE) of the control signal V_(CS) generated by the load control device 300 may be less than the rising threshold V_(TH-RISING). In some cases (such as, e.g., when a desired magnitude of the control signal V_(CS) is less than the rising threshold V_(TH-RISING) when power is applied to the LED light source 306), the control circuit 320 may be configured to temporarily increase the magnitude of the control signal V_(CS) to be equal to or greater than the rising threshold V_(TH-RISING) before decreasing the magnitude of the control signal V_(CS) to the desired magnitude. The control circuit 320 may be configured to determine when power is applied to the LED light source 306 (e.g., to the LED driver 304) in response to the magnitude (e.g., a change of the magnitude) of the control signal V_(CS) generated by the current sink circuit 310. For example, the LED driver 304 may be configured to generate a link supply voltage to allow the current sink circuit 310 to generate the control signal V_(CS) on the control wiring 308. As such, the magnitude of the control signal V_(CS) may indicate when the LED driver 304 is powered. For example, when the LED driver 304 is unpowered, the magnitude of the control signal V_(CS) may drop to approximately zero volts. When power is restored, the magnitude of the control signal V_(CS) may rise back to the level before power was lost. The control circuit 320 may be configured to determine that power has been lost and re-applied based on the changes (e.g., the drop and rise) in the magnitude of the control signal V_(CS).

The control circuit 320 may comprise a bump-up circuit 330 for temporarily increasing the magnitude of the control signal V_(CS) (e.g., when power is applied to the LED driver 304). FIG. 5 is a simplified diagram of example waveforms illustrating the operation of the bump-up circuit 330 of the load control device 300. The bump-up circuit 330 may comprise a bipolar junction transistor Q332 that may in turn include a collector coupled to an anode of a capacitor C334, the series combination of which is coupled between the first control terminal C1 and the wiper of the potentiometer circuit 322 (e.g., the DC output signal V_(DC) of the control circuit 320), with an emitter of the transistor Q332 coupled to the first control terminal C1, and a cathode of the capacitor C334 coupled to the wiper of the potentiometer circuit 322 and the current sink circuit 310. The bump-up circuit 330 may further comprise two resistors R336, R338 coupled in series between the first and second control terminals C1, C2. The tie point of the resistors R336, R338 may be coupled to the base of the transistor Q332.

When the magnitude of the control signal V_(CS) is approximately zero volts (e.g., the LED driver 304 is unpowered), the transistor Q332 may be non-conductive and the capacitor C334 may be uncharged. After power is applied to the LED driver 304, the LED driver 304 may begin to generate the link supply voltage (e.g., across the resistors R334, R336 of the bump-up circuit 330). Once the voltage across the resistor R334 exceeds the rated emitter-base voltage of the transistor Q332, the transistor may become conductive. When the transistor Q332 first becomes conductive, the capacitor C334 may be uncharged, and thus the transistor Q332 may pull the magnitude of the DC output signal V_(DC) up towards the magnitude at the first control terminal C1. This may cause the current sink circuit 310 to temporarily increase the magnitude of the control signal V_(CS) to be greater than the rising threshold V_(TH-RISING) (e.g., by an offset voltage V_(OFFSET)). As the capacitor C334 charges, the magnitude of the DC output signal V_(DC) may continue to fall until the capacitor C334 is fully charged and the magnitude of the DC output signal V_(DC) has returned to the level determined by the potentiometer circuit 322 and the intensity adjustment actuator 324 (e.g., the low-end magnitude V_(LE) as shown in FIG. 5). The bump-up circuit 330 may be configured to temporarily increase the magnitude of the control signal V_(CS) for a bump-up period T_(BUMP) (e.g., as shown in FIGS. 5). 

What is claimed is:
 1. A load control device for controlling a light-emitting diode (LED) driver for an LED light source, the load control device comprising: a communication circuit adapted to be coupled to the LED driver via a control wiring, the communication circuit configured to generate a control signal on the control wiring for controlling an intensity of the LED light source, the LED driver configured to turn on the LED light source when a magnitude of the control signal rises above a threshold; and a control circuit configured to control the communication circuit to adjust the magnitude of the control signal so as to adjust the intensity of the LED light source between a low-end intensity and a high-end intensity, the control signal having a magnitude less than the threshold when the intensity of the LED light source is being controlled to the low-end intensity; wherein, when power has been applied to the LED driver, the control circuit is configured to temporarily set the magnitude of the control signal to be greater than a desired magnitude of the control signal before decreasing the magnitude of the control signal to the desired magnitude.
 2. The load control device of claim 1, further comprising: an intensity adjustment actuator; wherein the control circuit comprises a potentiometer circuit responsive to the intensity adjustment actuator for determining the desired magnitude of the control signal.
 3. The load control device of claim 2, wherein the control circuit comprises a digital control circuit configured to determine that the desired magnitude of the control signal is below the threshold when power has been applied to the LED driver, control the communication circuit to set the magnitude of the control signal to be equal to or greater than the threshold if the desired magnitude of the control signal is below the threshold, and decrease the magnitude of the control signal to the desired magnitude over a first period of time.
 4. The load control device of claim 3, wherein the control circuit is configured to set the magnitude of the control signal to be equal to the threshold plus an offset amount if the desired magnitude of the control signal is less than the threshold when power has been applied to the LED driver.
 5. The load control device of claim 3, wherein the control circuit is configured to maintain the magnitude of the control signal constant at a level equal to or greater than the threshold for a second period of time when power has been applied to the LED driver before decreasing the magnitude of the control signal to the desired magnitude over the first period of time.
 6. The load control device of claim 3, further comprising: a sense circuit configured to provide an indication of when power has been applied to the LED driver.
 7. The load control device of claim 3, wherein the control circuit is configured to control the communication circuit to set the magnitude of the control signal to be equal to the desired magnitude if the desired magnitude of the control signal is greater than or equal to the threshold.
 8. The load control device of claim 2, wherein the control circuit comprises an analog control circuit that includes a bump-up circuit coupled to a wiper of the potentiometer circuit for increasing the magnitude of the control signal.
 9. The load control device of claim 8, wherein the bump-up circuit is configured to set the magnitude of the control signal to be equal to the desired magnitude plus an offset amount when power has been applied to the LED driver, and subsequently decrease the magnitude of the control signal to the desired magnitude.
 10. The load control device of claim 9, wherein the bump-up circuit is configured to maintain the magnitude of the control signal greater than or equal to the threshold for a period of time after power has been applied to the LED driver.
 11. The load control device of claim 1, further comprising: a switching circuit adapted to be electrically coupled in series between an AC power source and the LED driver; wherein the control circuit is configured to control the switching circuit to cause power to be applied to the LED driver.
 12. The load control device of claim 1, wherein the communication circuit comprises a current sink circuit.
 13. A method of controlling a light-emitting diode (LED) driver for an LED light source, the LED driver coupled to a control wiring for receiving a control signal, the method comprising: generating the control signal on the control wiring for controlling an intensity of the LED light source, the LED driver configured to turn on the LED light source when a magnitude of the control signal rises above a threshold; adjusting, after the LED light source has been turned on, the magnitude of the control signal so as to control the intensity of the LED light source between a low-end intensity and a high-end intensity, the magnitude of the control signal being equal to or less than the threshold when the intensity of the LED light source is being controlled to the low-end intensity; when power has been applied to the LED driver, temporarily setting the magnitude of the control signal to be greater than a desired magnitude of the control signal; and subsequently decreasing the magnitude of the control signal to the desired magnitude.
 14. The method of claim 13, further comprising, prior to temporarily setting the magnitude of the control signal to be greater than the desired magnitude of the control signal, determining that the desired magnitude of the control signal is below the threshold when power has been applied to the LED driver.
 15. The method of claim 14, wherein temporarily setting the magnitude of the control signal to be greater than the desired magnitude of the control signal further comprises: setting the magnitude of the control signal to be equal to or greater than the threshold if the desired magnitude of the control signal is below the threshold; and decreasing the magnitude of the control signal to the desired magnitude over a first period of time.
 16. The method of claim 15, wherein setting the magnitude of the control signal to be equal to or greater than the threshold further comprises setting the magnitude of the control signal to be equal to the threshold plus an offset amount if the desired magnitude of the control signal is less than the threshold when power has been applied to the LED driver.
 17. The method of claim 15, wherein temporarily setting the magnitude of the control signal to be greater than the desired magnitude of the control signal further comprises maintaining the magnitude of the control signal at a level equal to or greater than the threshold for a second period of time before being decreased to the desired magnitude over the first period of time.
 18. The method of claim 15, further comprising: sensing, via a sense circuit, that power has been applied to the LED driver.
 19. The method of claim 15, further comprising: setting the magnitude of the control signal to be equal to the desired magnitude if the desired magnitude of the control signal is greater than or equal to the threshold.
 20. The method of claim 13, wherein temporarily setting the magnitude of the control signal to be greater than the desired magnitude of the control signal further comprises: setting the magnitude of the control signal to be equal to the desired magnitude plus an offset amount when power has been applied to the LED driver; maintaining the magnitude of the control signal greater than or equal to the threshold for a period of time after power has been applied to the LED driver; and subsequently decreasing the magnitude of the control signal to the desired magnitude. 